AURORA, Colo., July 20 (Reuters) - A gunman in a gas mask and body armor killed 12 people at a midnight premiere of the new “Batman” movie in a suburb of Denver early on Friday, opening fire on moviegoers after hurling a gas canister into the theater.

Armed with an assault rifle, a shotgun and a pistol, he wounded 59 others with gunfire during a screening of “The Dark Knight Rises” at a mall in Aurora, which turned into a chaotic scene of bleeding victims, horrified screams and pleas for help, witnesses said.

Arriving on the scene within 90 seconds of the first emergency calls, police immediately took into custody the suspect, identified by police as James Eagan Holmes, 24, in a parking lot behind the cinema, where he surrendered without a fight, Aurora Police Chief Dan Oates said.

Holmes was due to make his first court appearance on Monday.

Police said Holmes also booby-trapped his Aurora apartment with what appeared to be sophisticated explosives, creating a potential hazard for law-enforcement and bomb squad officers who swarmed to the scene.

Authorities evacuated five nearby buildings and created a perimeter of several blocks as they planned to detonate the suspected explosives with a robot, a fire official said.

Witnesses at the movie theater reported chaos, with dazed victims bleeding from bullet holes, spitting up blood and crying for help. Among those taken to hospital as a precaution was a 3-month-old baby boy.

“I slipped on some blood and landed on a lady. I shook her and said, ‘We need to go, get up,’ and there was no response, so I presumed she was dead,” said Tanner Coon, 17. “I went toward the exit, waited in the exit for my friends and saw a guy with blood across his face and shoulders, and just got out of the movie theater.”

The shooting evoked memories of the 1999 massacre at Columbine High School in Littleton, also a Denver suburb and 17 miles (27 km) from Aurora, where two students opened fire and killed 12 students and a teacher.

‘PROBLEM ACROSS THE COUNTRY’

Other mass shootings in America have done little to encourage stricter gun control laws in a country where people jealously protect their right to bear arms. But New York Mayor Michael Bloomberg called for the U.S. presidential candidates to explain how they would address the issue.

“This is obviously a problem across the country,” said Bloomberg, who created a national organization called Mayors Against Illegal Guns.

The guns were legally purchased at three Colorado gun stores, according to a law enforcement official close to the investigation. Investigators found a drum magazine for the assault rifle with a capacity of about 100 rounds in the theater and a large amount of ammunition in his car, the source said, speaking on condition of anonymity.

President Barack Obama and his Republican presidential rival, Mitt Romney, toned down their campaigns, pulled their campaign ads from Colorado and dedicated their scheduled events to sympathy for the victims. Obama, who received a briefing on the shooting, pledged federal support for the investigation in a phone call with Oates, aides said.

“My daughters go to the movies,” Obama told supporters at a previously scheduled campaign event in Fort Myers, Florida. “What if Malia and Sasha had been at the theater as so many kids do each day?”

The suspect bought a ticket, entered the theater and propped open the emergency exit while he slipped out to “gear up” and return with arms, the law enforcement official said.

Holmes is a University of Colorado medical school student who was in the process of dropping out of a graduate program in neurosciences, the university said in a statement.

Smart and carrying himself with a swagger, he treated children kindly but had trouble finding work, people who knew him said.

But New York Police Commissioner Ray Kelly said he “clearly looks like a deranged individual.”

“He had his hair painted red, he said he was The Joker, obviously the enemy of Batman,” Kelly told reporters, referring to a character known for committing random, chaotic violence.

Holmes, who had only a speeding ticket on his police record, was dressed in black with a gas mask, ballistic helmet, vest, throat guard and crotch guard, Oates said.

His family issued a statement of sympathy for the victims, saying, “Our heart goes out” to their loved ones, while they also asked for privacy from the media while they “process this information.”

The living room of the suspect’s apartment was crisscrossed with trip wires connected to what appeared to be plastic bottles containing an unknown liquid, said Chris Henderson, Aurora’s deputy fire chief.

The suspect set a timer to turn on loud music in his apartment, apparently in an attempt to prompt a complaint and lure police into a trap, the law enforcement source said.

“If he was shot and killed, it is without a doubt that these ... booby traps were there to murder and inflict casualties upon first responders,” the source said.

SCENE OF BLOODY CHAOS

Confusion reigned as shooting broke out during an action scene in the summer blockbuster. The gunman may have blended in with other moviegoers who wore costumes as heroes and villains, and some witnesses said they first believed his appearance to be a theatrical enhancement to the film.

Chandler Brannon, 25, who had been watching the movie with his girlfriend, said that about 20 minutes into the movie he saw a smoke bomb go off and heard what sounded like fireworks. He later realized they were a rapid volley of gunshots.

“I told my girlfriend to just play dead,” he told Reuters.

“It was just straight chaos,” said Jennifer Seeger, 25. “Everybody was starting to scream and run at that point. He went straight from here to here with a gun in my face at that point, that rifle was in my face and I honestly didn’t know what to think.”

Bodies of victims remained in the theater while the investigation continued with some 200 local police, 100 FBI investigators and 25 representatives of the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives on scene, officials said.

U.S. military personnel were among the casualties. Two members of the Air Force and one Navy sailor were wounded, and another sailor known to have been at the theater was unaccounted for, the Defense Department said.

Buckley Air Force Base is the largest employer in Aurora, a city of more than 320,000 people, according to the Aurora Economic Development Council.

In New York, police pledged to deploy officers at all 40 theaters where “The Dark Knight Rises” was playing in the city “as a precaution against copycats” and to “raise the comfort level” of patrons, Kelly said. Los Angeles police also said they would increase patrols at “The Dark Knight Rises” and other popular movies.

Time Warner-owned Warner Bros., the studio behind the film, faced the prospect of seeing the blockbuster sink at box offices after the shooting, even as the film got off to a strong start across the United States and Canada.

The film, with a budget of $250 million, opened on 4,404 screens, the second-widest release ever behind “Twilight: Eclipse,” and industry analysts had said it stood a good chance of matching or beating the opening weekend box office record of $207 million set by Disney’s “Avengers” in May.